1. Field of the Invention
The present invention is broadly concerned with improved, high security switch apparatus, which can be used as a part of an alarm system responsive to unauthorized opening of a door or the like. More particularly, the invention is concerned with such apparatus which makes use of a ball-type magnetic switch assembly having an elongated housing and a magnetically shiftable ball therein. The ball traverses a path of travel between respective switch states which is oriented at an oblique angle relative to the horizontal, in order to prevent defeat of the alarm system through use of an external defeat magnet.
2. Description of the Prior Art
Prior art security alarm systems often make use of magnetic switches attached to doors and windows and integrated with the system for detecting unauthorized openings. One common type of magnetic switch used in these situations is a so-called reed switch. It has been found that reed switches are subject to unauthorized manipulation through use of an external magnet. Specifically, an intruder can hold a relatively strong magnet adjacent the reed switch which will then be operated (to either, open or close depending on the control scheme). With this accomplished, an intruder can open the door or window without triggering the alarm system.
A number of magnetic switches have been proposed in the past to overcome the inherent deficiencies of reed switches. U.S. Pat. Nos. 5,332,992, 5,530,428, 5,673,021, 5,880,659, 5,977,873, 6,506,987, 6,603,378, 7,023,308, 7,291,794, and 7,825,801 describe switches of this type. These switches typically include a pair of spaced apart switch elements with a shiftable body (e.g., a spherical ball) vertically movable within an upright housing between a first position where the ball is in simultaneous contact with both elements and a second position out of such simultaneous contact. An alarm circuit is operatively coupled with the switch elements so as to detect movement of the body. These switches represent a very significant advance in the art. The Magnasphere Corporation of Waukesha, Wis., has commercialized a series of magnetic switches of this type.
While magnetic ball switches of this type are greatly superior to reed switches, instances can arise when a very strong defeat magnet can be successfully used against alarm systems containing conventional magnetic ball switches. This may occur when the strong magnet is strategically placed so as to maintain the ball in its non-alarm switch state during the course of an illegal entry. There is accordingly a need in the art for an improved magnetic ball switch which makes it virtually impossible to defeat the switch using an external defeat magnet.